Effect of teosinte cytoplasmic genomes on maize phenotype

Improving the Carotenoid Content in Maize by Using Isonuclear Lines

Carotenoids are important biologically active compounds in the human diet due to their role in maintaining a proper health status. Maize (Zea mays L.) is one of the main crops worldwide, in terms of production quantity, yield and harvested area, as it is also an important source of carotenoids in human nutrition worldwide. Increasing the carotenoid content of maize grains is one of the major targets of the research into maize breeding; in this context, the aim of this study was to establish the influence of some fertile cytoplasm on the carotenoid content in inbred lines and hybrids. Twenty-five isonuclear lines and 100 hybrids were studied for the genetic determinism involved in the transmission of four target carotenoids: lutein, zeaxanthin, β-cryptoxanthin and β-carotene. The analysis of carotenoids was carried out using high performance liquid chromatography using a Flexar system with UV-VIS detection. The obtained data revealed that the cytoplasms did not have a significant influence on the carotenoid content of the inbred lines; larger differences were attributed to the cytoplasm × nucleus interaction. For hybrids, the cytoplasmic nuclear interactions have a significant influence on the content of lutein, zeaxanthin and β-cryptoxanthin. For the cytoplasm × nucleus × tester interactions, significant differences were identified for all traits.

Plastome genomics in South American maize landraces: chloroplast lineages parallel the geographical structuring of nuclear gene pools

BACKGROUND AND AIMS

The number of plastome sequences has increased exponentially during the last decade. However, there is still little knowledge of the levels and distribution of intraspecific variation. The aims of this study were to estimate plastome diversity within Zea mays and analyse the distribution of haplotypes in connection with the landrace groups previously delimited for South American maize based on nuclear markers.

METHODS

We obtained the complete plastomes of 30 South American maize landraces and three teosintes by means of next-generation sequencing (NGS) and used them in combination with data from public repositories. After quality filtering, the curated data were employed to search for single-nucleotide polymorphisms, indels and chloroplast simple sequence repeats. Exact permutational contingency tests were performed to assess associations between plastome and nuclear variation. Network and Bayesian phylogenetic analyses were used to infer evolutionary relationships among haplotypes.

KEY RESULTS

Our analyses identified a total of 124 polymorphic plastome loci, with the intergenic regions psbE-rps18, petN-rpoB, trnL_UAG-ndhF and rpoC2-atpI exhibiting the highest marker densities. Although restricted in number, these markers allowed the discrimination of 27 haplotypes in a total of 51 Zea mays individuals. Andean and lowland South American landraces differed significantly in haplotype distribution. However, overall differentiation patterns were not informative with respect to subspecies diversification, as evidenced by the scattered distribution of maize and teosinte plastomes in both the network and Bayesian phylogenetic reconstructions.

CONCLUSIONS

Knowledge of intraspecific plastome variation provides the framework for a more comprehensive understanding of evolutionary processes at low taxonomic levels and may become increasingly important for future plant barcoding efforts. Whole-plastome sequencing provided useful variability to contribute to maize phylogeographic studies. The structuring of haplotype diversity in the maize landraces examined here clearly reflects the distinction between the Andean and South American lowland gene pools previously inferred based on nuclear markers.

The History and Diversity of Rice Domestication as Resolved From 1464 Complete Plastid Genomes

The plastid is an essential organelle in autotrophic plant cells, descending from free-living cyanobacteria and acquired by early eukaryotic cells through endosymbiosis roughly one billion years ago. It contained a streamlined genome (plastome) that is uniparentally inherited and non-recombinant, which makes it an ideal tool for resolving the origin and diversity of plant species and populations. In the present study, a large dataset was amassed by de novo assembling plastomes from 295 common wild rice (Oryza rufipogon Griff.) and 1135 Asian cultivated rice (Oryza sativa L.) accessions, supplemented with 34 plastomes from other Oryza species. From this dataset, the phylogenetic relationships and biogeographic history of O. rufipogon and O. sativa were reconstructed. Our results revealed two major maternal lineages across the two species, which further diverged into nine well supported genetic clusters. Among them, the Or-wj-I/II/III and Or-wi-I/II genetic clusters were shared with cultivated (percentage for each cluster ranging 54.9%∼99.3%) and wild rice accessions. Molecular dating, phylogeographic analyses and reconstruction of population historical dynamics indicated an earlier origin of the Or-wj-I/II genetic clusters from East Asian with at least two population expansions, and later origins of other genetic clusters from multiple regions with one or more population expansions. These results supported a single origin of japonica rice (mainly in Or-wj-I/II) and multiple origins of indica rice (in all five clusters) for the history of rice domestication. The massive plastomic data set presented here provides an important resource for understanding the history and evolution of rice domestication as well as a genomic resources for use in future breeding and conservation efforts.

Characterization of cytoplasmic female sterility in an alloplasmic and monosomic addition line of Brassica rapa carrying the cytoplasm and one chromosome of Diplotaxis tenuifolia

Alloplasmic plants exhibit various phenotypic changes such as cytoplasmic male sterility (CMS). We have been attempting to produce an alloplasmic Brassica rapa CMS line (2n = 20) carrying Diplotaxis tenuifolia cytoplasm (cyt-Dt) for several years, but a single extra chromosome always remained in all lines produced. We confirmed a D. tenuifolia-specific band in the alloplasmic line carrying D. tenuifolia cytoplasm by RAPD analysis, indicating that the additional chromosome was derived from D. tenuifolia. Here, we observed the phenotypic characteristics of the alloplasmic B. rapa monosomic addition line, named (cyt-Dt) B. rapa MAL, and investigated why a single extra chromosome is required in its genetic background for viability. When the (cyt-Dt) B. rapa MALs were crossed with pollen of several B. rapa lines, approximately 50% of the ovules attracted pollen tubes, and all the progeny had the additional chromosome. These results suggested that only the female gametes with n = 11 rather than n = 10 were fertilized and developed into mature seeds, and that cytoplasmic female sterility was overcome by nuclear restorer gene(s) derived from the cytoplasmic donor species.

A Novel Chimeric Mitochondrial Gene Confers Cytoplasmic Effects on Seed Oil Content in Polyploid Rapeseed (Brassica napus)

Cytoplasmic effects (CEs) have been discovered to influence a diverse array of agronomic traits in crops, and understanding the underlying mechanisms can help accelerate breeding programs. Seed oil content (SOC) is of great agricultural, nutritional, and economic importance. However, the genetic basis of CEs on SOC (CE-SOC) remains enigmatic. In this study, we use an optimized approach to sequence the cytoplasmic (plastid and mitochondrial) genomes of allotetraploid oilseed rape (Brassica napus) cultivars, 51218 and 56366, that bear contrasting CE-SOC. By combining comparative genomics and genome-wide transcriptome analysis, we identify mitochondria-encoded orf188 as a potential CE-SOC determinant gene. Functional analyses in the model system Arabidopsis thaliana and rapeseed demonstrated that orf188 governs CE-SOC and could significantly increase SOC, strikingly, through promoting the yield of ATP. Consistent with this finding, transcriptional profiling with microarray and RNA sequencing revealed that orf188 affects transcriptional reprogramming of mitochondrial energy metabolism to facilitate ATP production. Intriguingly, orf188 is a previously uncharacterized chimeric gene, and the presence of this genetic novelty endows rapeseed with positive CE-SOC. Our results shed light on the molecular basis of CEs on a key quantitative trait in polyploid crops and enrich the theory of maternal control of oil content, providing new scientific guidance for breeding high-oil rapeseed germplasms.

Genetic diversity of submergence stress response in cytoplasms of the Triticum-Aegilops complex

Genetic diversity in cytoplasmic and nuclear genomes and their interaction affecting adaptive traits is an attractive research subject in plants. We addressed submergence stress response of wheat that has become increasingly important but remained largely uninvestigated. Our primary aim was to disclose cytoplasmic diversity using nucleus-cytoplasm (NC) hybrids possessing a series of heterologous cytoplasms in a common nuclear background. Effects of submergence on seedling emergence and growth from imbibed seeds were studied and compared with euplasmic lines. Marked phenotypic variabilities were observed among both lines, demonstrating divergent cytoplasmic and nuclear effects on submergence response. NC hybrids with cytoplasm of Aegilops mutica showed a less inhibition, indicative of their positive contribution to submergence tolerance, whereas cytoplasms of Aegilops umbellulata and related species caused a greater inhibition. Superoxide dismutase (SOD) activity showed a marked increase accompanied by retardation of seedling growth in a susceptible NC hybrid. The observation suggested that the elevated SOD activity was resulted from a high level of reactive oxygen species accumulated and remained in susceptible seedlings. Taken together, our results point to the usefulness of NC hybrids in further studies needed to clarify molecular mechanisms underlying the nucleus-cytoplasm interaction regulating submergence stress response in wheat.

Maize Cytolines Unmask Key Nuclear Genes That Are under the Control of Retrograde Signaling Pathways in Plants

The genomes of the two plant organelles encode for a relatively small number of proteins. Thus, nuclear genes encode the vast majority of their proteome. Organelle-to-nucleus communication takes place through retrograde signaling (RS) pathways. Signals relayed through RS pathways have an impact on nuclear gene expression but their target-genes remain elusive in a normal state of the cell (considering that only mutants and stress have been used so far). Here, we use maize cytolines as an alternative. The nucleus of a donor line was transferred into two other cytoplasmic environments through at least nine back-crosses, in a time-span of > 10 years. The transcriptomes of the resulting cytolines were sequenced and compared. There are 96 differentially regulated nuclear genes in two cytoplasm-donor lines when compared with their nucleus-donor. They are expressed throughout plant development, in various tissues and organs. One-third of the 96 proteins have a human homolog, stressing their potential role in mitochondrial RS. We also identified syntenic orthologous genes in four other grasses and homologous genes in Arabidopsis thaliana. These findings contribute to the paradigm we use to describe the RS in plants. The 96 nuclear genes identified here are not differentially regulated as a result of mutation, or any kind of stress. They are rather key players of the organelle-to-nucleus communication in a normal state of the cell.

The role of mitochondria in plant development and stress tolerance

Eukaryotic cells require orchestrated communication between nuclear and organellar genomes, perturbations in which are linked to stress response and disease in both animals and plants. In addition to mitochondria, which are found across eukaryotes, plant cells contain a second organelle, the plastid. Signaling both among the organelles (cytoplasmic) and between the cytoplasm and the nucleus (i.e. nuclear-cytoplasmic interactions (NCI)) is essential for proper cellular function. A deeper understanding of NCI and its impact on development, stress response, and long-term health is needed in both animal and plant systems. Here we focus on the role of plant mitochondria in development and stress response. We compare and contrast features of plant and animal mitochondrial genomes (mtDNA), particularly highlighting the large and highly dynamic nature of plant mtDNA. Plant-based tools are powerful, yet underutilized, resources for enhancing our fundamental understanding of NCI. These tools also have great potential for improving crop production. Across taxa, mitochondria are most abundant in cells that have high energy or nutrient demands as well as at key developmental time points. Although plant mitochondria act as integrators of signals involved in both development and stress response pathways, little is known about plant mtDNA diversity and its impact on these processes. In humans, there are strong correlations between particular mitotypes (and mtDNA mutations) and developmental differences (or disease). We propose that future work in plants should focus on defining mitotypes more carefully and investigating their functional implications as well as improving techniques to facilitate this research.

Cytonuclear interactions affect adaptive traits of the annual plant Arabidopsis thaliana in the field

Although the contribution of cytonuclear interactions to plant fitness variation is relatively well documented at the interspecific level, the prevalence of cytonuclear interactions at the intraspecific level remains poorly investigated. In this study, we set up a field experiment to explore the range of effects that cytonuclear interactions have on fitness-related traits in Arabidopsis thaliana To do so, we created a unique series of 56 cytolines resulting from cytoplasmic substitutions among eight natural accessions reflecting within-species genetic diversity. An assessment of these cytolines and their parental lines scored for 28 adaptive whole-organism phenotypes showed that a large proportion of phenotypic traits (23 of 28) were affected by cytonuclear interactions. The effects of these interactions varied from slight but frequent across cytolines to strong in some specific parental pairs. Two parental pairs accounted for half of the significant pairwise interactions. In one parental pair, Ct-1/Sha, we observed symmetrical phenotypic responses between the two nuclear backgrounds when combined with specific cytoplasms, suggesting nuclear differentiation at loci involved in cytonuclear epistasis. In contrast, asymmetrical phenotypic responses were observed in another parental pair, Cvi-0/Sha. In the Cvi-0 nuclear background, fecundity and phenology-related traits were strongly affected by the Sha cytoplasm, leading to a modified reproductive strategy without penalizing total seed production. These results indicate that natural variation in cytoplasmic and nuclear genomes interact to shape integrative traits that contribute to adaptation, thereby suggesting that cytonuclear interactions can play a major role in the evolutionary dynamics ofA. thaliana.

Plastid Genotyping Reveals the Uniformity of Cytoplasmic Male Sterile-T Maize Cytoplasms

Cytoplasmic male-sterile (CMS) lines in maize (Zea mays) have been classified by their response to specific restorer genes into three categories: cms-C, cms-S, and cms-T. A mitochondrial genome representing each of the CMS cytotypes has been sequenced, and male sterility in the cms-S and cms-T cytotypes is linked to chimeric mitochondrial genes. To identify markers for plastid genotyping, we sequenced the plastid genomes of three fertile maize lines (B37, B73, and A188) and the B37 cms-C, cms-S, and cms-T cytoplasmic substitution lines. We found that the plastid genomes of B37 and B73 lines are identical. Furthermore, the fertile and CMS plastid genomes are conserved, differing only by zero to three single-nucleotide polymorphisms (SNPs) in coding regions and by eight to 22 SNPs and 10 to 21 short insertions/deletions in noncoding regions. To gain insight into the origin and transmission of the cms-T trait, we identified three SNPs unique to the cms-T plastids and tested the three diagnostic SNPs in 27 cms-T lines, representing the HA, I, Q, RS, and T male-sterile cytoplasms. We report that each of the tested 27 cms-T group accessions have the same three diagnostic plastid SNPs, indicating a single origin and maternal cotransmission of the cms-T mitochondria and plastids to the seed progeny. Our data exclude exceptional pollen transmission of organelles or multiple horizontal gene transfer events as the source of the mitochondrial urf13-T (unidentified reading frame encoding 13-kD cms-T protein) gene in the cms-T cytoplasms. Plastid genotyping enables a reassessment of the evolutionary relationships of cytoplasms in cultivated maize.

Cytoplasmic genome substitution in wheat affects the nuclear-cytoplasmic cross-talk leading to transcript and metabolite alterations

Background

Alloplasmic lines provide a unique tool to study nuclear-cytoplasmic interactions. Three alloplasmic lines, with nuclear genomes from Triticum aestivum and harboring cytoplasm from Aegilops uniaristata, Aegilops tauschii and Hordeum chilense, were investigated by transcript and metabolite profiling to identify the effects of cytoplasmic substitution on nuclear-cytoplasmic signaling mechanisms.

Results

In combining the wheat nuclear genome with a cytoplasm of H. chilense, 540 genes were significantly altered, whereas 11 and 28 genes were significantly changed in the alloplasmic lines carrying the cytoplasm of Ae. uniaristata or Ae. tauschii, respectively. We identified the RNA maturation-related process as one of the most sensitive to a perturbation of the nuclear-cytoplasmic interaction. Several key components of the ROS chloroplast retrograde signaling, together with the up-regulation of the ROS scavenging system, showed that changes in the chloroplast genome have a direct impact on nuclear-cytoplasmic cross-talk. Remarkably, the H. chilense alloplasmic line down-regulated some genes involved in the determination of cytoplasmic male sterility without expressing the male sterility phenotype. Metabolic profiling showed a comparable response of the central metabolism of the alloplasmic and euplasmic lines to light, while exposing larger metabolite alterations in the H. chilense alloplasmic line as compared with the Aegilops lines, in agreement with the transcriptomic data. Several stress-related metabolites, remarkably raffinose, were altered in content in the H. chilense alloplasmic line when exposed to high light, while amino acids, as well as organic acids were significantly decreased. Alterations in the levels of transcript, related to raffinose, and the photorespiration-related metabolisms were associated with changes in the level of related metabolites.

Conclusion

The replacement of a wheat cytoplasm with the cytoplasm of a related species affects the nuclear-cytoplasmic cross-talk leading to transcript and metabolite alterations. The extent of these modifications was limited in the alloplasmic lines with Aegilops cytoplasm, and more evident in the alloplasmic line with H. chilense cytoplasm. We consider that, this finding might be linked to the phylogenetic distance of the genomes.

Unique changes in mitochondrial genomes associated with reversions of S-type cytoplasmic male sterility in maizemar

Cytoplasmic male sterility (CMS) in plants is usually associated with the expression of specific chimeric regions within rearranged mitochondrial genomes. Maize CMS-S plants express high amounts of a 1.6-kb mitochondrial RNA during microspore maturation, which is associated with the observed pollen abortion. This transcript carries two chimeric open reading frames, orf355 and orf77, both unique to CMS-S. CMS-S mitochondria also contain free linear DNA plasmids bearing terminal inverted repeats (TIRs). These TIRs recombine with TIR-homologous sequences that precede orf355/orf77 within the main mitochondrial genome to produce linear ends. Transcription of the 1.6-kb RNA is initiated from a promoter within the TIRs only when they are at linear ends. Reversions of CMS-S to fertility occur in certain nuclear backgrounds and are usually associated with loss of the S plasmids and/or the sterility-associated region. We describe an unusual set of independently recovered revertants from a single maternal lineage that retain both the S plasmids and an intact orf355/orf77 region but which do not produce the 1.6-kb RNA. A 7.3-kb inversion resulting from illegitmate recombination between 14-bp microrepeats has separated the genomic TIR sequences from the CMS-associated region. Although RNAs containing orf355/orf77 can still be detected in the revertants, they are not highly expressed during pollen development and they are no longer initiated from the TIR promoter at a protein-stabilized linear end. They appear instead to be co-transcribed with cytochrome oxidase subunit 2. The 7.3-kb inversion was not detected in CMS-S or in other fertile revertants. Therefore, this inversion appears to be a de novo mutation that has continued to sort out within a single maternal lineage, giving rise to fertile progeny in successive generations.

Influence of mitochondria on gene expression in a citrus cybrid

The production of cybrids, combining nucleus of a species with alien cytoplasmic organelles, is a valuable method used for improvement of various crops. Several citrus cybrids have been created by somatic hybridization. These genotypes are interesting models to analyze the impact of cytoplasmic genome change on nuclear genome expression. Herein, we report genome-wide gene expression analysis in leaves of a citrus cybrid between C. reticulata cv 'Willowleaf mandarin' and C. limon cv 'Eureka lemon' compared with its lemon parent, using a Citrus 20K cDNA microarray. Molecular analysis showed that this cybrid possesses nuclear and chloroplast genomes of Eureka lemon plus mitochondria from Willowleaf mandarin and, therefore, can be considered as a lemon bearing foreign mitochondria. Mandarin mitochondria influenced the expression of a large set of lemon nuclear genes causing an over-expression of 480 of them and repression of 39 genes. Quantitative real-time RT-PCR further confirmed the credibility of microarray data. Genes over-expressed in cybrid leaves are predominantly attributed to the functional category "cellular protein metabolism" whereas in the down-regulated none functional category was enriched. Overall, mitochondria replacement affected different nuclear genes including particularly genes predicted to be involved in mitochondrial retrograde signaling. Mitochondria regulate all cell structures even chloroplast status. These results suggest that nuclear gene expression is modulated with respect to new information received from the foreign organelle, with the final objective to suit specific needs to ensure better cell physiological balance.

Cytoplasmic-nuclear genomic barriers in rice pollen development revealed by comparison of global gene expression profiles among five independent cytoplasmic male sterile lines

Cytoplasmic male sterility (CMS) is one of the most ideal phenomena known in higher plants to describe the incompatibilities between mitochondrial-nuclear genomic interactions. To elucidate the dependency of pollen development on mitochondrial genotypes and cytoplasmic-nuclear genomic barriers, we employed five CMS isogenic lines of rice, CW-, W11-, LD-, BT- and WA-type CMS lines, that exhibit distinct pollen-defective phenotypes, and we characterized the CMS phenotypes and the nuclear gene expression patterns in conjunction with their mitochondrial genomic structures. These five CMS lines carried independent mitotypes, and W11, LD and BT mitochondrial genomes were relatively close with respect to their phylogeny. In anthers at the uninucleate microspore and bicellular pollen stages, 8,199 genes significantly changed their expression in at least one of the CMS lines. Common expression patterns were observed in BT, LD and W11 after k-means clustering. Among the genes encoding putative mitochondrial proteins, ALTERNATIVE OXIDASE 1A, a gene for the well-known mitochondrial stress marker, was included in the group ectopically up-regulated in anthers at the bicellular pollen stage of BT, LD and W11. Several other clusters were also regulated in a cytoplasm-specific manner during pollen development. These clear similarities in gene regulatory networks of BT-, LD- and W11-CMS lines indicate that the phylogenetic relationships of the mitochondrial genotypes are strongly correlated with nuclear gene expression patterns and pollen abortion phenotypes, providing evidence of the mitochondrial epistacy over the nuclear genome during pollen development.

Genetic analysis of nuclear-cytoplasmic incompatibility in pea associated with cytoplasm of an accession of wild subspecies Pisum sativum subsp. elatius (Bieb.) Schmahl

The genetic basis of nuclear-cytoplasmic incompatibility was examined using the wild pea (Pisum sativum subsp. elatius) accession VIR320. When this accession is used as the female parent in crosses with domesticated peas (Pisum sativum subsp. sativum) the F(1) is highly sterile and displays chlorophyll deficiency, chlorophyll variegation, reduction of leaflets and stipulae while the reciprocal cross produces hybrids that appear normal. A mapping recombinant inbred line (RIL) population was established based on a cross in a compatible direction of a tester line WL1238 with VIR320. The ability to cause nuclear-cytoplasmic conflict was analysed by crossing individual RIL plants as pollen parents with VIR320 as donor of cytoplasm and scoring each F(1) for major signs of the conflict. It is concluded that two unlinked nuclear genes are involved in the genetic control of the observed incompatibility. One of the genes, denoted as Scs1, is closely linked to the PhlC gene on linkage group III and the other, denoted as Scs2, is closely linked to the gp gene on linkage group V. Alleles of both genes in WL1238 are dominant and appear to be lethal in the homozygous condition in the VIR320 cytoplasm background.

Genetic dissection of cytonuclear epistasis in line crosses

Dissection of cytonuclear interactions is fundamentally important for understanding the genetic architecture of complex traits. Here we propose a mating design based on reciprocal crosses and extend the existing QTL mapping method to evaluate the contribution of cytoplasm and QTL x cytoplasm interactions to the phenotypic variation. Efficiency of the design and method is demonstrated via simulated data.

Comparisons among two fertile and three male-sterile mitochondrial genomes of maize

We have sequenced five distinct mitochondrial genomes in maize: two fertile cytotypes (NA and the previously reported NB) and three cytoplasmic-male-sterile cytotypes (CMS-C, CMS-S, and CMS-T). Their genome sizes range from 535,825 bp in CMS-T to 739,719 bp in CMS-C. Large duplications (0.5-120 kb) account for most of the size increases. Plastid DNA accounts for 2.3-4.6% of each mitochondrial genome. The genomes share a minimum set of 51 genes for 33 conserved proteins, three ribosomal RNAs, and 15 transfer RNAs. Numbers of duplicate genes and plastid-derived tRNAs vary among cytotypes. A high level of sequence conservation exists both within and outside of genes (1.65-7.04 substitutions/10 kb in pairwise comparisons). However, sequence losses and gains are common: integrated plastid and plasmid sequences, as well as noncoding "native" mitochondrial sequences, can be lost with no phenotypic consequence. The organization of the different maize mitochondrial genomes varies dramatically; even between the two fertile cytotypes, there are 16 rearrangements. Comparing the finished shotgun sequences of multiple mitochondrial genomes from the same species suggests which genes and open reading frames are potentially functional, including which chimeric ORFs are candidate genes for cytoplasmic male sterility. This method identified the known CMS-associated ORFs in CMS-S and CMS-T, but not in CMS-C.

Inheritance of organelle DNA markers in a pea cross associated with nuclear-cytoplasmic incompatibility

An unusual biparental mode of plastid inheritance was found in pea, in a cross associated with nuclear-cytoplasmic incompatibility manifested as deficiency of chlorophyll pigmentation. Plastid DNA marker trnK and mitochondrial DNA marker cox1 were analyzed in F1 progeny that received cytoplasm from an accession of a wild subspecies Pisum sativum ssp. elatius. Plants with sectors of green tissue on leaves and seed cotyledons with green patches on an otherwise chlorotic background were found to carry paternally inherited plastid DNA, suggesting that photosynthetic function was affected by nuclear-cytoplasmic conflict and required proliferation of paternally inherited plastids for normal performance. The paternally inherited plastid DNA marker was also observed in the roots. The presence of the paternal marker in cotyledons, roots and leaves was independent of each other. Inheritance of the mitochondrial DNA marker cox1 appeared to be of the maternal type.